transferable plasmids, which also contain virulence genes, such as the pUO-StVR plasmids in S. Typhimurium and the recently reported pUO-SeVR1 in S. Enteritidis [10,12,22]. Further studies of our isolates are needed to determine the plasmid localization of these ACSSuT resistance genes and/or their possible association with virulence genes. Class 1 integrons were present in 79% of the 90 isolates tested. Note the presence of a class 1 integron with the aac(6′) -Ib-cr+blaOXA-1+catB3+arr3 structure in the S. Thompson isolate. While this arrangement has been previously described, it is usually associated with complex integrons containing the ISCR1 elements, double copies of 3′-CS, and qnr genes, among others (e.g., GenBank accession numbers AJ971343 and AY259086). In addition, non-classical integrons (without qacEΔ1+sul1 genes) were found in three isolates (4%). All three included the gene cassette organization dfrA12+orfF +aadA2+cmlA1+aadA1, in two of these three isolates in association with the qacH+IS440+sul3 structure previously reported in Salmonella and E. coli [1,25]. In conclusion, blaPSE-1 and blaOXA-1 were the most frequent bla genes implicated in the AMCR/I phenotype in S. Typhimurium, and blaTEM-1 the most frequent in S. Enteritidis. ESBLpositive isolates, corresponding to non-S. Typhimurium serotypes, were identified in <1% of the S. enterica isolates obtained from the three hospitals. Among the three different ESBL variants detected, ours is the first description of CTXM-15 in S. Gnesta. In addition, the frequent association of the β-lactamase production with nalidixic acid resistance (22%), which precludes the use of fluoroquinolones in the treatment of salmonellosis, is a cause for clinical concern and underlines the need to track the evolution of β-lactamases in S. enterica isolates. Acknowledgements. We thank M. Aurora Echeita from the Centro Nacional de Microbiología, Instituto de Salud Carlos III, Madrid, Spain, for serotyping of the isolates. M. de T. is the recipient of a predoctoral fellowship from the Instituto de Salud Carlos III of Spain (MINCINN) (grant number FI08/00506). Competing interests. None declared.
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INT. MICROBIOL. Vol. 14, 2011
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